To assess the cutoff values at different time points for impaired glucose regulation (IGR) and diabetes, the glucose curve and isolated 1-h hyperglycemia were monitored during an oral glucose tolerance test (OGTT).

Two thousand eight hundred and eighty-six subjects (1300 men and 1586 women) were recruited to have an OGTT. Plasma was collected at 0, 30, 60, 120, and 180 min to analyze glucose and insulin. The diagnosis of impaired fasting glucose, impaired glucose tolerance, and diabetes was based on World Health Organization and American Diabetes Association's criteria. Those with fasting plasma glucose (FPG)<5.6 and 2-h plasma glucose (PG)<7.8, but 1-h PG≥7.8 and <11.1 mmol/l were defined as 1h-High7.8, and those with FPG<7.0 and 2-h PG<11.1, but 1-h PG≥11.1 mmol/l as 1h-High11.1. The cutoff values were calculated by receiver operating characteristic (ROC) curve. The correlation between β-cell function and the area under the curve of glucose (AUCg) and the shape index was analyzed with linear regression.

The cutoff values for IGR were 5.6, 9.7, 10.1, 7.8 and 6.1 mmol/l for blood glucose at 0, 30, 60, 120 and 180 min, 24 for AUCg and 1.3 mmol/l for the shape index. The cutoff values for diabetes were 6.8, 11.2, 13, 11.1 and 7 mmol/l for 0, 30, 60, 120 and 180 min, 30.9 for AUCg and 2 mmol/l for the shape index. Both AUCg and the shape index were inversely related to β-cell function. The profiles of glucose and insulin in the subgroup with isolated 1-h hyperglycemia were very different from those seen in subjects with normal glucose tolerance or IGR.

The present study provides new information on measures other than the fasting and 2-h PG to evaluate glucose metabolism in vivo and stimulates further research aimed at assessing the value of the OGTT 1-h PG concentration prospectively.